Ben331

Hey guys new to true forum I got a f150 with the 5.4 I have changed the iac, maf, idle air temp sensor, the pcv nd checked for vaccum leaks the best I can and still can’t figure out what’s wrong with the thing it is surging at idle nd I have both lean bank codes from the 02 sensors any one got any other ideas what could cause this

Jbrew

Do you know which model year ?

Most likley the PCV assembly, The assembly tube likes to leak back by the firewall just behind the intake. You can't see it, but you can get your hand back there. While it's running and surging, follow the PCV line back there with your hand. Move the tube around or plug the hole with your finger temporarily. Idle will change while doing so.

It's either that or bad manifold leak...doubt that, but possible.

9918939

Jbrew-
IF it is a manifold leak- would the rpm surge be consistent or (in my case) after the engine warms up the idle surge stops? Thanks

jprevat

iTrader: (1)

I would say that depends on your ambient air temperature. If the engine warms up and then idle improves I would say gasket or rubber became less rigid. get a small propane bottle with a burner tip and point it (unlit and opened up) all around the hoses and intake and see where the idle changes.